Re: [gtk-vnc-devel] Fix mmap permissions for coroutine stacks

[Anthony Liguori <anthony codemonkey ws>]

Daniel P. Berrange wrote:
> Our current code mmaps a region with PROT_EXEC for use as stack space in 
> the swapcontext() calls. This is bogus because the stack should not be
> executable. On any Fedora / RHEL system with SELinux enabled this results
> in the process being terminated with extreme prejudice the moment we do
> the swapcontext() call.
>
> The attach patch removes the use of PROT_EXEC, and it also switches to use
> MAP_PRIVATE instead of MAP_SHARED since ther is no reason for stack to be
> shared across processes, and finally removes MAP_GROWSDOWN since it is a
> broken concept that should not be used according to GLibC guys.
>   

Very interesting patch.   GROWSDOWN seemed like the Right Thing to do 
but I'm not surprised if it's broken.  Removing EXEC seems sane to me.  
It was just a guess as what the right permissions should be.

BTW, if the coroutine stuff ever gets too weird, we can very easily 
switch over to lock-step threads.  I know that there's been some 
concerns about the portability of coroutines in the context of the gnome 
community before (gstreamer initialized used a coroutine mechanism).  
I'd still want to stick with lock-step execution of threads b/c I think 
it simplifies locking.

Any thoughts?

Regards,

Anthony Liguori

> I notice that there have been a few mysterious crash reports in the Vinagre
> bugzilla  which could well be explained by this bug, so it'd be worth getting
> the users in question to try this patch too.
>
> Dan.
>   
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